This invention relates to a system for monitoring the condition of a plurality of fluids, and more particularly, for determining the condition of the various fluids by measuring electrical characteristics of fluid samples and generating, storing, and monitoring historical record signals representative of the determined condition of the various fluids.
It is well known that the functional effectiveness of many commercially used fluids degrades substantially through use as the result of contaminants in the fluids. For example, lubricating oils lose their effectiveness in lubricating mechanical assemblies as contaminants such as dirt, water, acids, oxidation products, varnish, and anti-freeze enter the oil during use. In view of this, it has become common practice to frequently change the lubricating oil in many mechanical assemblies, such as internal combustion engines, in order to prolong the life of such mechanisms. For example, automobile manufacturers generally recommend a change of engine oil after a certain period of operation, typically 2,000 to 4,000 miles in order to maintain a relatively contaminant-free oil. However, that approach, whereby the oil is changed under a rigid use-related change schedule, does not accommodate variations in the rate at which the oil may be contaminated for individual engines, such as may be based on particular factors associated with the individual engines. As a result, the lubricating oil in many engines and other mechanical assemblies is often changed even though the original oil still has satisfactory lubricating properties, in one extreme, or, in the other extreme, at a time well beyond that where the oil has lost its lubricating properties, resulting in possible damage to the engine.
As a further example, the commercially used cooking oil in deep fat frying apparatus degrades through use due to the accumulation of contaminants such as dirt, water, food particles, and other debris. Typically, in commercial practice, the oil is replaced on a rigid, use-related change schedule, regardless of the actual condition of the oil.
In order to offset the inefficiencies of a rigid use-related schedule, instruments have been developed for testing the condition of such fluids by periodically sampling the fluid and measuring the contaminant level in the samples. By way of example, it is known that typical lubricating oils used in internal combustion engines may be characterized by a dielectric coefficient which is generally proportional to the concentration of suspended foreign matter (such as dirt, water, acids, varnish and anti-freeze) and the level of oxidation of the oil. Similarly, the dielectric coefficient of many commercial cooking oils are also proportional to the contaminant content of those oils. Accordingly, those dielectric coefficients may be considered as a measure of the contaminant level. U.S. Pats. Nos. 3,182,255 and 3,331,019 describe two such instruments suitable for measuring the dielectric coefficient of a sample of lubricating oil, and thereby provide a measure of the contaminant level of that sample.
While the instruments described by the above-referenced patents do set forth a sensor and coupled electrical circuit means to generate a test signal representative of the dielectric constant of a fluid sample applied to the sensor, those instruments only provide an indication of the contamination level for a single sample at a time. As a result, the use of these instruments often requires that extensive historical data records be maintained in order to efficiently maintain an on-going monitoring of the condition of fluids associated with a large number of assemblies. For example, individual vehicle lubricating oil condition records for truck fleets are often established with the manual recording of raw test data provided by the contaminant level measuring instruments. These records must then be tediously updated and monitored to identify those mechanical assemblies in which the lubricating oil contaminant level has passed a danger level.
Accordingly, it is an object of the present invention to provide a system for automatically monitoring the condition of a plurality of fluids, as determined from the measured electrical characteristics of samples of those fluids successively applied to a sensor.
It is another object of the present invention to provide a system whereby one or more remote test terminals may sample and generate test signals representative of the current characteristics of a plurality of fluids, and wherein those test terminals operate in conjunction with a central controller which maintains historical records for each of the fluids as obtained by interrogating the various remote terminals.